msc patran gap elements

LESSON 5

(1) (2) (3)

(4) (5)

Gap Elements

P

P

www.cadThe docu

Objectives:

■ Use of GAP contact elements

■ Small deformation theory

■ Varying contact condition

PATRAN 322 Exercise Workbook 5-1

family.com EMail:[email protected] is for study only,if tort to your rights,please inform us,we will delete

www.cadfamily.com

5-2 PATRAN 322 Exercise Workbook

www.cadfamily.com EMail:[email protected] document is for study only,if tort to your rights,please inform us,we will delete

www.cadfamily.com

LESSON 5 Gap Elements

www.cThe do

Model Description:Three parallel cantilever beams are initially separated, but havepossible contact points in five locations, as shown in the figure onthe following page. A pair of pinching loads is applied, as shown.The pinching loads are increased from no load at the beginning ofthe step, to full load, 200 lbs, at the end of the step. Only smalldisplacements are considered, so that each beam responds in purebending. The problem is entirely linear, except for the switchingcontact conditions. The sequence of events is readily imagined:

1. The top and bottom beams bend as the pinching forces are applied, and the first contact occurs when the tip of the top beam hits the tip of the middle beam (gap 3 closes). Up to this point the problem is symmetric about the middle beam, but it now loses that symmetry.

2. Subsequent to this initial contact, the top and middlebeams bend down and the bottom beam continues tobend up, until contact occurs at gap 5.

3. As the load continues to increase, gap 2 closes.

4. Next, gap 3 opens, as the support provided to the topbeam by gap 2 causes the outboard part of the top beamto reverse its direction of rotation. At this point (whengap 3 opens), the solution becomes symmetric about themiddle beam once again.

5. Finally, as the pinching loads increase further, gaps 1and 4 also close. From this point on, the contactconditions do not switch, no matter how much more loadis applied.

Initially all gaps are open, with an initial gap clearance of 0.01. Thepinching loads are increased monotonically from 0 to 200. The beamlengths, modulus, and cross-section are shown on the followingpage.


adfamily.com EMail:[email protected] is for study only,if tort to your rights,please inform us,we will delete

www.cadfamily.com

www.cadThe doc

.

Suggested Exercise Steps:

■ Create a new database and name it gapuni.db.

■ Change your analysis code preference to P3⁄ADVANCED FEA.

■ Create the 3 lines 50 units long, and mesh each of them with 5 cubic beam elements.

■ Specify material properties and element properties.

■ Apply the loads and boundary conditions.

■ Analyze the model and post process the results.

0.01”

Circumscribing radius = 0.50”

wall thickness = 0.10”

Material Properties

E = 108 force/length2

ν = 0.10

gap A

A

P

P

Length = 50. units

3”



www.cadfamily.com


www.cThe do

Exercise Procedure:1. Create a new database named gapuni.db.

2. The viewport will appear along with a New ModelPreference form. The New Model Preference sets allthe code specific forms inside MSC/PATRAN. In theNew Model Preference form set the analysispreference to MSC/ADVANCED FEA.

3. Create the geometry for the model using the curve XYZoption with <50, 0, 0> for the vector and [0 0 0], [0 3 0],and [0 6 0] for the starting points.

First, turn on the entity labels using the following toolbar icon:

For Curve 1.

For Curve 2 and 3 modify the Origin Coordinates List to read[0 3 0] and [0 0 0] respectively.

File/New ...

Database Name: gapuni.db

OK

Analysis Code: MSC/ADVANCED_FEA

OK

◆ Geometry

Action: Create

Object: Curve

Method: XYZ

Vector Coordinates List: <50 0 0>

Origin Coordinates List: [0 6 0]

Apply

Show Labels



www.cadfamily.com

www.cadThe doc

These curves will represent the three beams for this example. Yourmodel should appear as shown in Figure 6.1:

Figure 6.1 - Three beams

4. Create a new group, fem, to hold all the FEM entities.Make it the current group.

5. Mesh the three beams with 10 as the global length,choose bar 2 elements.

Group/Create ...

New Group Name: fem

■ Make Current

Apply

Cancel

◆ Finite Elements

Action: Create

Object: Mesh



www.cadfamily.com


www.cThe do

Your model should appear as shown in Figure 6.2:

Figure 6.2 - Three beams meshed with bar elements

6. Create group gap and make it current. It will hold thegap elements.

Type: Curve

Global Edge Length: 10

Element Topology: Bar2

Curve List: select all three curves

Apply

Group/Create ...

New Group Name: gap

■ Make Current

❐ Unpost All Other Groups



www.cadfamily.com

www.cadThe doc

7. Create the gap elements between the node pairs (2, 8),(4, 10), (6, 12), (8, 14), (10, 16). These are modeled withBar2 elements.

Your model should now look like the one shown in Figure 6.3:

Apply

Cancel

◆ Finite Elements

Action: Create

Object: Element

Method: Edit

Shape: Bar

Topology : Bar2

Pattern: Standard

Node1: Node 2, 4, 6, 8, 10

Node2: Node 8, 10, 12, 14, 16

Apply



www.cadfamily.com


www.cThe do

Figure 6.3 - Beams with gap elements

Note: It should be noted that the creation direction of all the barelements, (u2 - u1), is in the negative Y direction. Thisdirection will be used later when we define the contactclosure direction under Element Properties. To review,contact closure is defined below:

h

n

h d n u2 u1–( ) 0≥⋅+=node 1

node 2



www.cadfamily.com

www.cadThe doc

8. Create the material, beam_material. It is elastic, withYoung’s Modulus of 1E8, and Poisson’s Ratio of 0.10.

9. Post the beam finite element group, fem.

10. Create the element property, beam_prop. The thicknessis 0.1, the direction is the global y direction, the materialis the beam_material. This is applied to the beamelements only.

◆ Materials

Action: Create

Type: Isotropic

Method: Manual Input

Material Name : beam_material

Input Properties...

Constitutive Model: Elastic

Elastic Modulus: 1E8

Possion’s Ratio: 0.10

Apply

Cancel

Group/Post ...

Select Groups to Post: fem

Apply

Cancel

◆ Properties

Action: Create

Dimension: 1D

Type: Beam in XY Plane

Property Set Name: beam_prop

Options:

Hexagonal Section



www.cadfamily.com


www.cThe do

In the Application Region part of the Element Properties form, clickin the Select Members databox. The select menu will appear. Selectthe icon for the Beam elements as shown below.

Select all posted entities in the viewport. This should correspond toelements 1:15.

11. Post the gap finite element group, gap.

12. Create the element property, gap_prop. The initialclearance is 0.01, the direction is <0 -1.0 0>. This isapplied to the gap elements only.

Cubic Interpolation

Input Properties...

Material Name: beam_material

Circumscribing Radius: 0.5

Wall Thickness: 0.1

OK

Add

Apply

Group/Post ...

Select Groups to Post: gap

Apply

Cancel

Action: Create

Dimension: 1D

Type: Gap

Property Set Name: gap_prop

Beam Elements



www.cadfamily.com

www.cadThe doc

Note: Remember, the opening/penetration of the gap contact isdetermined by comparing the relative displacements of thenodes in the contact direction, n, to a user specified initialdistance, d. The gap opening can be defined by:

The relative displacements of the nodes are defined by the nodeordering of the bar elements, node 1 and node 2 (which correspondsto u1 and u2). The normal direction, n, of the closure is defined inthe form above.

In the Application Region part of the Element Properties form, clickin the Select Members databox. The select menu will appear. Selectthe icon for the Beam elements as shown below.

Select all posted entities in the viewport. This should correspond toelements 16:20.

13. Create a new group all_fem.

This group will have all the finite elements for the entire model in it.

Options:

Uniaxial

True Distance

Input Properties...

Initial Clearance: 0.01

Vector: <0 -1.0 0>

OK

Add

Apply

Group/Create ...

New Group Name: all_fem

■ Make Current

■ Unpost All Other Groups

h d n u2 u1–( ) 0≥⋅+=

Beam Elements



www.cadfamily.com


www.cThe do

14. Create the loads and boundary conditions. The ends arefixed in all three translations and rotations.

First, fit the display to the model using the following toolbar icon:

Group Contents: Add All FEM

Apply

Cancel

◆ Load/BCs

Action: Create

Object: Displacement

Type: Nodal

New Set Name: fixed_end

Input Data...

Translations <T1,T2,T3>: <0, 0, >

Rotations <R1,R2,R3>: < , , 0>

OK

Select Application Region...

Geometry Filter: ◆ FEM

Select Nodes: see Figure 6.4

Fit View



www.cadfamily.com

www.cadThe doc

Figure 6.4 - Fixed ends of beams

15. Create a force on node 3 pointing down and a force onnode 15 pointing up. The force vectors are <0, -200, 0>and <0, 200, 0> for node 3 and 15, respectively.

Add

OK

Apply

Action: Create

Object: Force

Type: Nodal

New Set Name: down

Input Data...

Force <F1,F2,F3>: < , -200, >

OK

Select Application Region...

Geometry Filter: ◆ FEM

Select Nodes: see Figure 6.5

X

Y

Z

1 2 3 4 5 6

7 8 9 10 11 12

13 14 15 16 17 18

1 2 3 4 5

6 7 8 9 10

11 12 13 14 15

16 17 18

19 20

X

Y

Z

Screen select leftedge nodes of each bar



www.cadfamily.com


www.cThe do

Click in the Select Nodes databox and select Node 3 in the middle ofthe top beam as in Figure 6.5:

Figure 6.5 - Load application locations

Similarly, create a second load applied to node 15 in the oppositedirection with the name of up. The force vector will be < ,200, >,and the application region is Node 15 in the middle of the bottombeam as shown in Figure 6.5.

16. Ready the model for analysis. Create an analysis stepcalled pinching_load. For this analysis step, you will beusing the default load case and default output requests.

Add

OK

Apply

◆ Analysis

Action: Analyze

Object: Entire Model

Method: Full Run

X

Y

Z

1 2 3 4 5 6

7 8 9 10 11 12

13 14 15 16 17 18

1 2 3 4 5

6 7 8 9 10

11 12 13 14 15

16 17 18

19 20

126

126

126

X

Y

Z

Upper load application node

Lower load application nodeNode 15

Node 3

LBC Name = down

LBC Name = up



www.cadfamily.com

www.cadThe doc

17. Create an analysis job and submit it. You will need toselect the pinching_load step and unselect the defaultstatic step. Only the pinching_load step should appearin the selected job steps.

18. From another UNIX shell, monitor the analysis bymonitoring the .sta and .msg files. When the jobs arefinished, read in the results.

Job Name: gapuni

Step Creation...

Job Step Name: pinching_load

Solution Type: Nonlinear Static

Solution Parameters...

Large Deflection/Strains: OFF

Riks Method: OFF

Automatic Load Increment: OFF

Delta-T: 0.1

Time duration for this step: 1.0

OK

Apply

Cancel

Step Selection...

Selected Job Steps: pinching_load

Apply

Apply

Action: Read Results

Select Results File...

Available Files: gapuni.fil

OK

Apply



www.cadfamily.com


www.cThe do

19. Change the scale of the deformation on the Results form

Select the Deformation Attributes icon from the Results form

20. Create a deformed plot from the results.

Click on the Select Results icon

The plot should look like the one shown in Figure 6.6:

◆ Results

Action: Create

Object: Quick Plot

Scale Factor: 0.05

◆ Model Scake

Select Results Case: select the last increment of step 1,time = 1.0

Select Fringe Result: None

Select Deformation Results: Deformation, Displacement

Apply



www.cadfamily.com

www.cadThe doc

Figure 6.6 - Deformed beams with gap elements

21. Generate a report to get the forces to complete the table.

The final step in this assignment is to fill in the chart on thefollowing page.

X

Y

Z

12

34

5

6

7 8 9 10 11 12

1314

1516

17

18

12 3

4

5

6 7 8 9 10

1112 13

14

15

16 17

18

19 20

126

200.0

126

126

200.0

Z



www.cadfamily.com


www.cThe do

To get the data for the above table, you will generate a reportwith all the gap results.

To get the results for the gap elements, those elements need to be inthe current group.

Be sure you are on the Select Results form, click on View Subcasethen Subcase Select

Table 1: Summary chart of gap forces for each analysis increment

IncrementPinching

force,P

Force in gap

1 2 3 4 5

1

2

3

4

5

6 120 Open 59.82 Open Open 59.82

7

8

9

10

Group/Set Current ...

Set Current Group: gap

Cancel

◆ Results

Select Results View Subcase Subcase Select



www.cadfamily.com

www.cadThe doc

The results will be printed to the UNIX window that you started P3up in.You will need to find that shell and get your results from there.You will get one page of results for each increment. Each page ofresults contains results for each gap element for that increment.Below is an example of the results produced for increment 6

===================================================================2.1-Force and Shear Forces, Components

Load case 6 = Default, Step1,TotalTime=0.6 - Lid 3 = (NON-LAYERED)

LAYR ELEM EPOS SYS XX-COMP YY-COMPZZ-COMP XY-COMP YZ-COMP XZ-COMP

3 16 2 ELEM 0.000000 0.0000000.000000 0.000000 0.000000 0.000000

17 2 ELEM 59.819271 0.0000000.000000 0.000000 0.000000 0.000000

18 2 ELEM 0.000000 0.0000000.000000 0.000000 0.000000 0.000000

19 2 ELEM 0.000000 0.0000000.000000 0.000000 0.000000 0.000000

20 2 ELEM 59.819271 0.0000000.000000 0.000000 0.000000 0.000000

The XX Component indicates the normal force that is transmittedacross the gap. If the value is zero, the gap is not transmitting anyforce, and therefore would be an indication that the gap is open.

To find out how much the gaps are open, you could plot the result“4.1-Rel. Displacements and Shear Slips, Components”. Again, theXX column indicates the amount the gap is open in the normaldirection.

Filter method: All

Filter

Apply

Close

Select Results: Force and Shear Forces

Apply



www.cadfamily.com


www.cThe do

Question 1: How would you model an Elasto-plastic gap? Note that as the gap deformations are in the plastic range, the initial gap size increases.

____________________________________________

____________________________________________

____________________________________________

____________________________________________

____________________________________________

Question 2: How would you define the gap closure direction for a set of coincident nodes.

____________________________________________

____________________________________________

____________________________________________

____________________________________________

____________________________________________.

You may now quit PATRAN.

Force

initialgap size

deformation

New Gap Size

Elasto-Plastic Force vs. Deflection Curve



www.cadfamily.com

www.cadThe doc

This concludes this exercise.

Table 2: Answers for Table 1

Increment Pinching force,

P

Force in gap

1 2 3 4 5

1 20 Open 6.50 0.73 Open 7.97

2 40 Open 18.34 Open Open 18.34

3 60 Open 28.71 Open Open 28.71

4 80 Open 39.08 Open Open 39.08

5 100 Open 49.45 Open Open 49.45

6 120 Open 59.82 Open Open 59.82

7 140 10.71 68.60 Open 10.71 68.60

8 160 31.61 75.88 Open 31.61 75.88

9 180 52.52 83.15 Open 52.52 83.15

10 200 73.43 90.42 Open 73.43 90.42



www.cadfamily.com

msc patran gap elements

Documents